1. Field of the Invention
The present invention relates to an inkjet printer, and more particularly, to a paper feeding mechanism for transferring sheets of paper to an inkjet printer for printing, and a method for using the same.
2. Description of the Related Art
As can be appreciated by one skilled in the art, to perform a printing operation, an inkjet printer transfers a sheet to a printing zone, ejects ink on the sheet via a print head in which ink cartridges are mounted to print characters or images, and discharges a printed sheet out of the main body of the printer. A conventional inkjet printer of this type includes a paper supply cassette, a pickup roller, a drive roller, a feed roller, a discharge roller, and a print head.
The paper supply cassette stores sheets of paper, and the pickup roller is disposed to rotate while contacting the upper surface of a topmost sheet loaded in the paper supply cassette. The drive roller is located in the middle of a paper transfer path connecting the leading edge of the paper supply cassette and the feed roller, and transfers to the feed roller a sheet picked up by the pickup roller.
The feed roller is located ahead of the print head, and, in conjunction with a print head guide bar, aligns the sheet transferred from the drive roller so as to cause the leading edge of that sheet to be supplied in parallel with the travel direction of the print head. The feed roller thus positions the aligned sheet beneath the printing head.
The print head ejects ink through nozzles while traversing along the guide bar that is parallel with the feed roller, thereby printing characters and images on the sheet. The discharge roller is mounted in the paper travel path past the print head, and discharges the sheet after the printing has been completed by the print head.
An inkjet printer having the above structure operates as follows.
If the pickup roller rotates, the topmost sheet of the stack of sheets loaded in the paper supply cassette is separated and transferred to the drive roller. The drive roller transfers to the feed roller the sheet picked up by the pickup roller. The feed roller aligns the sheet to enable the sheet transferred from the drive roller to be supplied in parallel with the guide bar. At this time, a technique for aligning the printing sheet employs a general technique in which the feed roller reverse-rotates to backwards transfer the printing sheet toward the drive roller by a certain distance, and then forward-rotates.
In order to align a printing sheet in such a manner, the feed roller needs to perform reverse and forward rotations. However, the drive roller or the discharge roller needs only to perform only a unidirectional rotation. Accordingly, these types of printers typically employ a driving source for the feed roller and a separate driving source for the drive roller, or alternatively, employ a clutch to interrupt power transferred to the drive roller as needed to enable the feed roller to reverse-rotate and forward-rotate as necessary. In this configuration, the discharge roller is generally mounted to be driven in association with the driving source for the feed roller.
However, an inkjet printer that uses a clutch to interrupt the drive roller has the following problems.
First, when the feed roller aligns a sheet for printing, the drive roller can not transfer a picked-up sheet to the feed roller because rotation of the drive roller is stopped when the feed roller is reverse-rotated during the aligning operation.
Second, before the distal end of a sheet completely comes out of the discharge roller when being discharged from the printer after being printed on, the feed roller cannot align the sheet transferred from the drive roller because the sheet being discharged is reverse-transferred toward the feed roller when the discharge roller is reverse-rotated as the feed roller is reverse-rotated.
Third, sheets of paper cannot be continuously supplied. In order to continuously supply sheets, when the end of a sheet picked up by the pickup roller passes through the drive roller, the pickup roller should pick up a new sheet and then pass the newly picked-up sheet to the drive roller. However, when the distal end of the previous sheet passes through the drive roller and the leading edge of the new sheet passes into the feed roller, the drive roller is in a stopped state during the time that the feed roller reverse rotates to align the sheet. Accordingly, sheets are not supplied continuously, and the inkjet printer experiences a low printing speed, in other words, a low number of printed sheets per minute.
Furthermore, although the first and third problems discussed above do not occur when a separate driving source drives the drive roller, the problem of low printing speed still remains. In addition, the use of a separate driving source raises the manufacturing cost of the printer, and requires more space for installing the additional driving source, which increases the overall size of the printer.